The coastguard said a search of only the first two of the 14 containers carried by the Bolivian vessel Haddad 1 had revealed almost 500,000 rounds of ammunition and 5,000 shotguns, of a type similar to that used by police, with no accompanying documentation.

They were found at the bottom of the containers, concealed by a load of furniture, including drawers, cupboards, and a layer of gymnastic mats.

The Haddad 1, a rusty 65-metre vessel built in 1976 and registered in the port of La Paz, was intercepted off Ierapetra, southeast of Crete, earlier this week, as it was heading to the Libyan city of Misrata.

It had left the southern Turkish port of Iskenderun, about 50km from the Syrian border a few days earlier.

Its crew of seven has been arrested, while inspectors continued searching the remaining containers in the port of Crete’s largest city, Iraklion. Greek authorities have not released their nationalities, which local media say include Syrians, Egyptians and Indians.

Greek Marine Minister Christos Zois praised the “professionalism” of the coastguard for the identification of the ship, adding the investigation was ongoing and further information would be released at a later stage. “The count of weapons and ammunition is continuing and we hope that soon we will have more information on this case,” he said.

It was not immediately clear who the cargo was being shipped to. The port of arrival, Misrata, is controlled by Libya Dawn, an Islamist umbrella group that took over the capital, Tripoli, last year, ousting the internationally recognised government and installing a rival administration.

Greek media however suggested the Islamic State (Isis) local offshoot, a rival of Libya Dawn, based in nearby Sirte was to be the final recipient.